(a) Field of the Invention
This invention relates to improvements in a compound carburetor to be used for an internal combustion engine of a plurality of cylinders.
(b) Description of the Prior Art
In a compound carburetor to be used for an engine of a plurality of cylinders, a primary air-fuel mixture passes through one throttle valve and is then distributed to respective cylinders, a secondary air-fuel mixture is fed to the respective cylinders through secondary throttle valves arranged for the respective cylinders and a secondary slow-running fuel system for controlling the air-fuel ratio at the beginning of opening of the secondary throttle valves is provided to smooth the transit from the primary side of the secondary side. However, in this type of conventional compound carburetor, generally, there have been defects that, as one secondary slow-running fuel system is distributed to the secondary throttle valves of the respective cylinders, due to the fluctuation of the opening of the secondary throttle valve for each cylinder, the fluctuation of the opening area of the secondary bypass hole, the difference in the length and bend of the secondary slow-running mixture path and the air locking phenomenon in the course of the secondary slow-running mixture path likely to occur at a high temperature which are all difficult to technically solve, the air-fuel ratio of the mixture for each cylinder will fluctuate in the course of the transit from the primary side to the secondary side and the transit will be no longer smooth. Further, generally, the carburetor body is sectioned into a carburetor portion, a manifold portion and a throttle body portion and is formed by combining them. However, the above mentioned secondary slow-running fuel system or particularly the secondary slow-running mixture path is formed within these respective portions, is therefore comparatively long in the total length and can not help having many bends. Not only this will be likely to cause an air locking phenomenon when the engine temperature rises as described above but also it will increase the flow resistance to cause the delay of the transit from the primary side to the secondary side and the unstable jet of the mixture. Therefore, in order to shorten the total length of the secondary slow-running mixture path and to decrease the bends, it has been already attempted to arrange the carburetor portion and throttle body portion in the same plane. However, there have been defects that this arrangement will not only increase the useless thickness of the component parts but also require a large space and cause a leakage due to different strains of the respective portion by heat.